1. Field of the Invention
This invention relates generally to a cable lubricating apparatus. In particular, this invention relates to an apparatus for supplying a lubricant to a fiber optic cable and an improved method of introducing the lubricant into a conduit through which the fiber optic cable will be pulled.
2. Description of the Prior Art
Wire lubricating devices are well known in the prior art. The basic concept of introducing a lubricant onto the surface of a wire is disclosed, for example, in U.S. Pat. No. 296,440, issued to Oliver. Oliver discloses the use of a cylinder "a" with an opening at each end, thereby permitting the introduction and removal of the cable from the cylinder in one continuous strand. The lubricant used is oil, which is introduced onto the surface of the wire through the medium of sawdust. The sawdust is packed in the cylinder and surrounds the cable as it is pulled through the device. The Oliver device is designed primarily to assist in the manufacture of barbed wire, and does not address the problems associated with placing a cable inside a closed, inaccessible conduit.
One attempt at solving the problem of depositing a lubricant into an inaccessible location is disclosed in U.S. Pat. No. 1,253,837, issued to Keating. The Keating patent uses a revolving tube 20, to force the lubricant down a shaft in order to reach inaccessible bearings. The lubricant introduced into the tube is designed only to reach the bearing 6. The problem of coating a continuous cable or wire with lubricant is not addressed.
Another example of a rope lubricating device is disclosed in U.S. Pat. No. 1,584,704, issued to Swan. The Swan disclosure utilizes a fibrous material 15 which absorbs lubricant from chamber 12, the lubricant being applied to the rope 16 as the rope is pulled past the fibrous sponge 15. The Swan device is designed to solve the problem of preventing abrasive contact between a relatively rough rope or cable 16 and a relatively large metal casing within which the rope resides. Swan does not disclose a method of uniformly coating a cable which is in contact with a conduit at substantially every point around its circumference.
Taken together, these previously described devices embody the basic components present in every cable lubricating apparatus. The results obtained with such simple devices are unsatisfactory, and each component of these devices has been the subject of intensive efforts at improvement, with the goal of improving the overall cable lubricating system. Each of these components will now be briefly discussed.
First, most cable lubricating devices utilize some resilient medium, such as sawdust, cork or sponge, to transfer the lubricant to the cable.
The problem of applying uniform and adequate sponge pressure to the cable being lubricated has long perplexed cable lubricator designers. For example, U.S. Pat. No. 1,102,965, issued to Smith, discloses a funnel shaped cable lubricator. The housing 1 is open at both ends to allow the introduction and removal of a single cable. The housing is shaped as a funnel to facilitate adding lubricant to the housing, but this structure necessitates use of the lubricator only in a vertically upright position. The effects of gravity tend to concentrate the lubricant at the bottom of the funnel, thereby partially negating the effect of having the large surface area of the sponge in contact with the cable.
One method of overcoming the effects of gravity when using a liquid lubricant is to place the cable lubricating device in a horizontal position. U.S. Pat. No. 1,049,170, issued to Thomas, discloses a relatively long horizontal casing 3 through which a cable or rope may be pulled. The Thomas device introduces a relatively uncontrolled amount of lubricant to the cable as it enters the channel 6, and utilizes various wiper brushes and a storage tube 29 to remove the excess lubricant as the cable is pulled through the channel. The excess lubricant must be continuously removed through valve 32 and reintroduced into funnel 12 in order to prevent excessive lubricant consumption.
All of the devices thus far mentioned have relied solely on gravity to supply the pressure needed to deposit lubricant on the cable. Often, however, the vertical separation between the lubricant reservoir and the cable to be coated is too small to create the pressure head needed to supply an adequate amount of lubricant to the cable.
One solution to this problem is disclosed in U.S. Pat. No. 2,201,803, issued to Todd, which uses a wick 28 to bring the lubricant material into close proximity with the cable 32. By moving the cable past the wick, a combination of electrostatic and aerodynamic forces attract the lubricant away from the wick and cause it to be deposited onto the surface of the cable. This system is effective, however, only when the cable can be moved by the wick at a relatively high speed. Also, in some cases, electrical grounding of the apparatus may be required to achieve the desired effect.
A similar utilization of the "suctional" effect of a moving cable is disclosed in U.S. Pat. No. 2,435,120, issued to Baker (column 2, lines 22-25).
In some cases, the amount of lubricant applied to the cable can be increased somewhat by the application of mechanical pressure to the sponge like material which contacts the cable. One attempt to increase the amount of lubricant transferred from a sponge-like material to a cable is disclosed in U.S. Pat. No. 1,589,108, issued to Caretta. The Caretta device utilizes a spring 10 which presses packing material 8 against the walls of lubricant containing sleeve 6. The use of the spring 10 tends to improve the quality of the seal at each end of the sleeve, and also increases the pressure of the packing material 8 against the surface of cable 5. The Caretta device, however, is designed only to coat a relatively small portion of the cable which is repeatedly pulled back and forth through the sleeve as part of a mechanical transmission device. Thus, the same small length of cable is repeatedly exposed to the lubricant, which tends to lessen the effect of any shortcomings in the lubricant application system.
Another example, U.S. Pat. No. 2,531,095, issued to Williams, discloses the use of resilient clip 24 to press saturated sleeve 18 against the cable 10. U.S. Pat. No. 2,604,650, issued to Mottelson, utilizes the pressure of a human hand to control the amount of pressure exerted by a split sponge 14 against cable 16, although in this case the sponge is used to remove material from the cable rather than to deposit lubricant.
The most common method of increasing the pressure of the lubricant against the cable within a cable lubricating device is to utilize a mechanical pump. U.S. Pat. No. 3,733,216, issued to Goldman, et al., shows the use of pump 5 to forcibly introduce and remove lubricant into channels 8 and 9.
U.S. Pat. No. 3,783,972, issued to Molstad, utilizes hand pump 25 to force a lubricant into cylindrical enclosure 16, thereby coating cable 18.
U.S. Pat. No. Re. 29,493, issued to Crump, utilizes a pump to direct fluid under high pressure onto a cable. In this particular device, the fluid is used to scour the cable in a cleaning operation, rather than for lubrication.
Other methods of applying a lubricant to a cable include the use of magnetic attraction between the lubricant and the cable, as disclosed in U.S. Pat. No. 3,851,623, issued to Landry, Jr. (column 4, lines 19-22).
Another common problem with cable lubricating devices is the inability of the device to uniformly coat the entire surface area of the cable. If the cable is readily accessible, one solution is to periodically coat the cable with an additional layer of lubricant. Such a device, designed to be used with motorcycle control cables and other cables which are exposed to an unprotected environment, is disclosed in U.S. Pat. No. 4,039,048, issued to Safholm. The Safholm device, however, is useful only for cables which may be removed and placed into a special lubricating apparatus.
A similar device for use in the field is disclosed in U.S. Pat. No. 4,042,065, issued to Crum, but this device is useful only for the very specialized purpose of relubricating the pin and bushing which interconnects the individual track lengths on a track-type vehicle.
Rather than attempt to relubricate a device in the field, a preferable solution for use with cables which will reside in a protected environment is to uniformly deposit the lubricant onto the cable during the initial application. U.S. Pat. Nos. 4,063,617 and 4,046,225, both issued to Shenk, disclose a conventional cable lubricating device in which the cable application sponges consist of split annular discs. The slits in the disc are rotatably displaced, and the discs themselves are longitudinally displaced so that the cable must pass through each of the discs during the lubricating process. The use of three discs tends to spread the lubricant evenly about the surface of the cable.
U.S. Pat. No. 4,326,605, issued to Conti, uses a series of bristles 19 located downstream from the point of initial lubricant application to uniformly spread the lubricant onto the surface of the cable. U.S. Pat. No. 4,336,866, issued to Blanton, Jr. utilizes a rotatable, mechanical die to remove excess lubricant and uniformly redistribute the lubricant that remains on the cable surface.
Other cable lubricating devices are designed to solve the problem of lubricating an inaccessible or stationary cable. U.S. Pat. No. 3,889,781, issued to Schott, et al., discloses a clamping fixture which may be attached to a cable at which time lubricant may be applied under pressure to a small section of the cable. This device anticipates that the cable will be housed in a relatively accessible environment rather than in a conduit.
U.S. Pat. No. 3,951,235, issued to Acerbi, discloses a device which can automatically lubricate cables when the cable system is in motion throughout its normal operation, such as in an elevator shaft or on a cable operated crane. The Acerbi device utilizes plate 33 to apply constant pressure to grease 39 as the supply of lubricant within the reservoir diminishes.
U.S. Pat. No. 4,169,427, issued to Crump, et al., discloses a lubricating device which travels along a stationary cable. Rollers 85, 86, 87 and 88 are utilized to transport the device along the cable.
U.S. Pat. No. 4,069,894, issued to Black, discloses a manually operated tool which is capable of reaching and lubricating cables in relatively inaccessible locations. The Black device utilizes an extendable handle 20 and a swiveling head 18 which permits sponge 24 to engage cable 26 and be moved manually along the portion of the cable where lubrication is desired.
Most relevant to the present invention are those devices which have attempted to solve the problem of providing lubrication to a cable which must be pulled through a conduit. One such method and apparatus is disclosed in U.S. Pat. No. 3,858,687, issued to Masarky, et al. Masarky utilizes small packets 12 of lubricant which are adhesively attached to the surface of the cable at various intervals. As the cable is pulled through the conduit, the packets are torn open and a lubricant is released. Such a lubricating system is complicated by the requirement that the packets must be individually applied to the cable surface. There is no assurance that lubricant will be provided where most needed, or that not all of the lubricant will be exhausted prior to finishing the pulling of an electrical cable through a conduit.
Other solutions to the problem or placing a cable in conduit utilize a lubricant dispensing apparatus which travels in the conduit ahead of the cable. U.S. Pat. No. 4,108,279, issued to Marcell, utilizes a dispenser 21 which is pulled through the conduit by piston assembly 30, thereby leaving a coating of lubricant on the inside of the conduit prior to the passage of the cable.
U.S. Pat. No. 4,275,096, issued to Taylor, discloses a method and apparatus utilizing cartridges. The cartridge 10 is pulled through conduit 18, the lubricant 48 being absorbed by core 28 and the excess being collected in chamber 46, where it may be reabsorbed by core 28 as the supply of lubricant within the core is periodically exhausted. A similar cartridge based device is disclosed by Taylor in his U.S. Pat. No. 4,137,623.
Each of the prior art devices described thus far have attempted to apply uniform coating of lubricant on a cable. In some applications, particularly where the cable does not reside within a conduit, a uniform coating of lubricant on a cable may be the optimum solution to the problem posed by a cable which must periodically slide past pulleys, bearings or casings.
An optimized cable lubricating device will deposit a disproportionately large amount of lubricant onto the front of the cable during the early stages of the cable pull and will deposit a relatively small amount of lubricant at the back end of the cable. Ideally, this should be accomplished without the use of pumps, brushes, wipers, or other mechanical contrivances which require external power or add mechanical complexity to the lubricating system. The problem of finding a simple method of lubricating a cable is particularly acute when fiber optic cable must be placed within a conduit, because fiber optic cable is relatively difficult to splice in the field. Therefore, many fiber optic cable installations involve pulling the cable a distance of thousands of feet without interruption, often without intermediate access to the cable, and at remote locations where power sources necessary for the operation of mechanical brushes or pumps is simply not available. Thus, while the devices of the prior art may have been satisfactory for their intended purposes, when they are applied to fiber optic cable installations, they are inadequate because of their complex design, cost, and labor intensive manner of use.